1. Field of Invention
The present invention relates to a digital image processing method and a device using the same, and more particularly to a method of generating a high dynamic range (HDR) image and a digital image pickup device using the same.
2. Related Art
When sensing the lights, the visual system of the human eye adjusts its sensitiveness according to the distribution of the ambient lights. Therefore, the human eye may be adapted to a too-bright or too-dark environment after a few minutes' adjustment. Currently, the working principles of the image pickup apparatus, such as video cameras, cameras, single-lens reflex cameras, and Web cameras, are similar, in which a captured image is projected via a lens to a sensing element based on the principle of pinhole imaging. However, the photo-sensitivity ranges of a photo-sensitive element such as a film, a charge coupled device sensor (CCD sensor), and a complementary metal-oxide semiconductor sensor (CMOS sensor) are different from that of the human eye, and cannot be automatically adjusted with the image. Therefore, the captured image usually has a part being too bright or too dark. FIG. 1 is a schematic view of an image with an insufficient dynamic range. The image 10 is an image with an insufficient dynamic range captured by an ordinary digital camera. In FIG. 1, an image block 12 at the bottom left corner is too dark, while an image block 14 at the top right corner is too bright. In such a case, the details of the trees and houses in the image block 12 at the bottom left corner cannot be clearly seen as this area is too dark.
In the prior art, in order to solve the above problem, a high dynamic range (HDR) image is adopted. The HDR image is formed by capturing images of the same area with different photo-sensitivities by using different exposure settings, and then synthesizing those captured images into an image comfortable to be seen by the human eye. FIG. 2 is a schematic view of synthesizing a plurality of images into an HDR image. The HDR image 20 is formed by synthesizing a plurality of images 21, 23, 25, 27, and 29 with different photo-sensitivities. This method achieves a good effect, but also has apparent disadvantages. First, the position of each captured image must be accurate, and any error may result in difficulties of the synthesis. Besides, when the images are captured, the required storage space rises from a single frame to a plurality of frames. Moreover, the time taken for the synthesis is also considered. Therefore, this method is time-consuming, wastes the storage space, and easily gets wrong.
Further, in the prior art, when an image processing is performed to simulate an HDR image, an image bloom is usually generated. FIG. 3 is a schematic view of an image bloom. When simulating the HDR image 30, the brightness of too-dark areas in the image is raised, and meanwhile the texture of the image should be maintained, so that the brighter parts in these too-dark areas are made even brighter, and thus the image texture effect may not be weakened due to the brightening of the too-dark areas. However, this method may also enhance the brightness at the borders 32 of the too-dark and too-bright areas, thus resulting in an image bloom.